1. Field of the Invention
The present invention relates to the field of controlling the environment in the cabin or other locations in an aircraft. More specifically, the present invention relates to systems and methods for controlling cabin temperatures where high pressure air is bled from the engine of the aircraft for the purpose of maintaining cabin pressure.
2. Description of the Related Art
Cabin pressures in some aircraft have traditionally been maintained by bleeding high pressure air from the compressor section of a gas turbine engine on the aircraft. The high pressure of this bleed air is ramped down using a flow control valve consisting of a pressure regulator and a flow control nozzle. The bleed air is then introduced into the cabin at a constant flow rate. To ensure that desired cabin pressure limits are not exceeded, the cabin includes one or more electronically controlled pressure relief valves which release cabin air to control cabin pressure to a predetermined level. Thus, the cabin pressure is maintained constant.
Although these traditional arrangements adequately handle cabin pressures, climate control problems result. Bleed air temperatures are normally very high, and thus, the bleed air must be cooled in order to maintain cabin air temperatures at pleasant levels.
One conventional approach is to dispose of heat using a heat exchanger in the bleed air passageway which runs from the engine to the cabin. This heat exchanger, however, is useful only when the aircraft is in flight because it draws ram air from an air scoop on the outside of the aircraft. When the aircraft is stationary, the scoop provides no forced air. Thus, the heat exchanger will have no effect because there is no cross flow.
When in flight in cold ambient temperatures, these conventional arrangements can effectively maintain temperatures in the cabin. On hot days, however, a separate air conditioning system must be used to further cool the cabin below ambient temperatures. This is because the heat exchanger is dependent on outdoor temperatures for cooling. Thus, where outside temperatures are above what is desirable, this air as a cooling medium for the heat exchanger is not sufficient to cool the bleed air running through the exchanger. And the problem is even greater when the aircraft is on the ground and no ram air is available.
Because the heat exchanger alone is not able to handle all possible environmental conditions, a separate air conditioning system is normally provided to maintain cabin temperatures. In most cases a vapor cycle cooling system is used. This added equipment requires extra space, adds weight to the aircraft, and is very expensive. On hot days—especially when the aircraft is stationary, the air conditioning system for the aircraft is greatly burdened, and the vapor cooling systems also require significant electrical energy. Thus, there is a need in the art for a system that overcomes these and other deficiencies in the conventional arrangements.